1. Field of the Invention
This invention generally relates to electrochemical cells and, more particularly, to a battery formed from an alkali anode and cathode including nickel or iron.
2. Description of the Related Art
A battery is an electrochemical device in which electrons and ions commute between the anode and cathode to realize electrochemical reactions. The voltage and capacity of the battery are determined by the electrode materials. In a conventional battery, all the components including anode materials, cathode materials, separator, electrolyte, and current collectors are packed into a volume-fixed container. Its energy and capacity of are unchangeable as long as the battery is assembled. A flow-through battery consists of current collectors (electrodes) separated by an ion exchange membrane, while its anode and cathode materials are stored in separate storage tanks. The anode and cathode materials are circulated through the flow-through battery in which electrochemical reactions take place to deliver and to store energy. Therefore, the battery capacity and energy are determined by (1) electrode materials (anolyte and catholyte), (2) the concentrations of anolyte and catholyte, and (3) the volumes of anolyte and catholyte storage tanks. Conventional state-of-the-art anode and cathode materials typically react with an aqueous or non-aqueous solution (electrolyte) containing some redox couples.
In general, the use of metals as anode materials can achieve a high voltage in the battery while their low molecular weight provides a large capacity. For example, lithium has the most negative potential of −3.04 volts (V) vs. H2/H+ and the highest capacity of 3860 milliamp hours per gram (mAh/g). High voltage and large capacity lead to an overall high energy for the battery. In addition, sodium, potassium, magnesium, nickel, zinc, calcium, aluminum, etc. are good candidates as the anode materials in metal-ion batteries.
The state-of-the-art cathode materials focus on the metal-ion host compounds. Metal-ions can be extracted from the interstitial spaces of the electrode materials in the charge process and inserted into the materials during the discharge process. However, it is worth noting that the charge/discharge process severely distorts the lattice of the materials, which essentially destroys their structures following several cycles. Moreover, these cathode materials can only provide less than one tenth capacities of the metal anode materials. Therefore, new cathode materials need to be developed in order to (1) match the higher capacities of the anode materials and (2) exhibit long cycle lives for the metal-ion batteries.
In 1996, Abraham and Jiang reported a polymer electrolyte-based rechargeable lithium/oxygen battery in which oxygen was used as the cathode material1. Oxygen in air continuously flowed into the battery and provided a very high specific energy of 5200 watt hours per kilogram (Wh/kg). Nevertheless, the oxygen cathode has several disadvantages. Firstly, expensive electro-catalysts were used in the batteries to reduce the kinetic barrier for the oxygen reactions. Secondly, the sluggish electrochemical reactions of oxygen produce a large overpotential in the lithium/air battery. Thirdly, the lithium/air battery must maintain an open cathode to allow air access. Similarly, an oxygen cathode was also used in the zinc-air batteries2.
In 2011, Lu and Goodenough revealed an aqueous cathode for a lithium ion battery3. They used aqueous solutions of water-soluble redox couples, for example, Fe(CN)63−/Fe(CN)64− as the cathode. The lithium/aqueous cathode battery operated at ca. 3.4 volts in an ambient environment. The battery demonstrated a small overpotential, a high coulombic efficiency, and a long cycle life. However, water is an inert material in the electrochemical system, which reduces the specific capacity of the cathode. Although the design of a lithium/flow-through cathode battery can increase the capacity and energy, its volume must necessarily be large.
With the similar battery structure, Ni(OH)2 was used as the cathode to match a lithium anode4. The Li/Ni(OH)2 battery has to be charged so that Ni(OH)2 can be oxidized to NiOOH along the reaction:Ni(OH)2+OH−=NiOOH+H2O+e−.
At the same time, the following reaction occurs:Li++e−=Li
in which lithium-ions come are sourced from the electrolyte. Therefore, the battery capacity is limited by the Li-ion concentration in electrolytes, although Ni(OH)2 experimentally demonstrate a high capacity of 260 mAh/g. The capacity advantage of the Li/Ni battery is limited by the Li-ion concentration in the electrolyte.
It would be advantageous if NiOOH could be used as the cathode material in a battery with a lithium anode, so that the capacity of a Li/Ni battery is determined by the amount of NiOOH in the cathode at fabrication.
[1] K. M. Abraham, Z. Jiang, “A polymer electrolyte-based rechargeable lithium/oxygen battery”, Journal of the Electrochemical Society, 143 (1996) 1-5.
[2] Philip N. Ross, Jr., “Zinc electrode and rechargeable zinc-air battery”, U.S. Pat. No. 4,842,963.
[3] Yuhao Lu, john B. Goodenough, Youngsik Kim, “Aqueous cathode for next generation alkali-ion batteries” Journal of the American Chemical Society, 133 (2011), 5756-5759.
[4] H. Li, Y. Wang, H. Na. H. Liu, H. Zhou, “Rechargeable Ni-Li battery integrated aqueous/nonaqueous system”, J. Am. Chem. Soc, 131 (2009) 15098-15099.
[5] William C. Carter, Yet-Ming Chiang, “High energy density redox flow device”, US 2011/0189520.